Recently, a retinal-protein complex has been identified in Halobacterium halobium membranes, with the function of a light-driven translocator of sodium ions. It is proposed to search for purity and characterize the protein(s) which constitute this pump: that which binds the retinal and any others involved in function. Functional reconstitution of the pump protein(s) into lipid vesicles will be pursued. The photointermediates produced by flash illumination will be described in relation to the ion translocation steps. Comparisons with bacteriorhodopsin will contribute to understanding how retinal-proteins function, and to the general field of membrane ionic pumps.